This invention relates to thermonuclear fusion electrical power generation and specifically, to a method and system for producing electrical current directly from the lithium blanket region of a magnetically confined, deuterium-tritium (DT) fueled, thermonuclear fusion reactor.
At the present time magnetically confined thermonuclear fusion reactors have not yet been fully developed for practical application in energy production. Although experimental magnetically confined thermonuclear fusion reactors have been constructed and fusion energy released, no reactor has achieved the necessary goal of self-sustained thermonuclear ignition and bum of a plasma, nor reached the easier and more preliminary "break-even" experimental milestone in which the released fusion energy equals the necessary investment of energy in plasma heating and confinement. Nevertheless, these goals are being pursued by ongoing experimental research and have been approached when using geometric arrangements for magnetic confinement of the plasma producing a set of toroid shaped, closed "magnetic surfaces" nested inside each other and filling the plasma volume. There are several slightly different competing versions of these toroidal magnetic geometry arrangements, e.g., the tokamak, the symmetrical torus (ST), the reversed-field pinch (RFP), the stellarator, and the torsatron, among others. At the present time, significant fusion energy release has only been achieved in the tokamak magnetic geometry using a plasma consisting of a mixture of deuterium and tritium (DT) fuels.
FIG. 1 illustrates the general three dimensional geometric arrangement of magnet components typically used in such toroidal magnetic confinement thermonuclear fusion reactors, emphasizing the approximate rotational symmetry of the arrangement. It shows the outer toroidal "magnetic surface" of the confined plasma, which in the tokamak version is nearly axisymmetric about a geometric center line A--A. It also shows a set of toroidal field (TF) electromagnet coils which link the plasma, and various axisymmetric poloidal field (PF) electromagnet coils which do not link the plasma. In a tokamak, multiple identical TF electromagnet coils are used and distributed uniformly in a rotationally symmetrical manner about the center line A--A, thus forming a quasiaxisymmetric set. An external electrical power control system causes electrical current to flow in each of these TF electromagnet coils. The total overall spatial distribution of electrical currents in the TF electromagnetic coils, and the plasma, naturally produces the confining magnetic field in the plasma's toroidal region, according to the fundamental physical laws of electromagnetism.
Many variations of the device geometry shown in FIG. 1 are possible, including the mechanical construction of the TF electromagnets as shown but consisting of demountable subassemblies; simple noncircular deformations of the electromagnet coil shapes; and even complicated nonplanar helical hybrid combinations of the PF and TF electromagnets.
Components not shown in FIG. 1 include a (nonmagnetic) vacuum vessel which is needed to keep air away from the plasma. The vacuum vessel typically has a toroidal shape in order to enclose the plasma, and is located between the plasma and the TF electromagnet coils.
Additionally, the fusion blanket or alternatively the liquid metal blanket, which is believed to be necessary for practical energy production from fusion, is not depicted. At the present time, fusion blankets have been proposed, but no fusion blanket has yet been successfully tested for an experimental, operational thermonuclear fusion reactor. Because most of the released thermonuclear fusion energy will exit the plasma in various forms of radiation, e.g., neutrons, x-rays, gamma rays, etc., the fusion blanket must consist of a material of suitable type and thickness to completely absorb such radiation, thus converting the radiation directly to heat in the blanket material or liquid metal. Since the radiation will exit the plasma in all directions, this fusion blanket must completely enclose the toroidal plasma. To avoid losing radiation energy in useless and counterproductive heating of the electromagnets and vacuum vessel, the fusion blanket must necessarily be located adjacent to the plasma, i.e., inside the TF electromagnet coils and vacuum vessel and be capable of absorbing the radiation.
For a self-sufficient DT reactor, the fusion blanket must also produce the tritium component of the plasma fuel, and the reactor system must breed at least as much tritium as it consumes. This requirement, in turn, dictates that any DT fusion blanket must be largely or completely composed of lithium, the only element which can efficiently produce tritium when it absorbs the neutron radiation resulting from DT fusion in the plasma.
Technical provisions are necessary to continuously transfer and harvest heat from the fusion blanket for electrical power production. Perhaps the simplest imaginable method becomes possible if the blanket material is mostly composed of liquid lithium itself or alternatively some lithium-bearing liquid. Then the liquid blanket material can be pumped around a loop, cycling between the blanket region where it is automatically heated by radiation from the plasma, and a different (and possibly remote) region where the heat is extracted from the liquid and electrical power is produced.
Conventional methods for producing electric power from a heat source employ "balance-of-plant" equipment consisting of a rotating electrical generator mechanically driven by an engine, such as a turbine or a reciprocating piston system, in turn mechanically driven by a thermodynamic working fluid such as steam. For many conventional methods, including methods used with nuclear fission heat sources, heat exchange components provide thermal coupling between the heat source and the working fluid, and additional heat exchangers reject waste heat from the working fluid to the external environment.
Liquid metal magnetohydrodynamic (LMMHD) electrical power generation from an unspecified generic heat source has previously been proposed as a simple and robust method for efficiently producing electrical power. Such proposals have examined various possible 2-phase LMMHD working fluids, including the combined 2-phase lithium/helium working fluid of the present invention. While coupling LMMHD power generation to a thermonuclear fusion reactor heat source has likewise been proposed, the hybrid features of the present method, which are peculiar to a magnetically confined deuterium-tritium (DT) fueled thermonuclear fusion reactor, have not been previously published or claimed.
Accordingly, a first object of the present invention is to provide an improved method and system for producing electric power from a thermonuclear fusion reactor that is not as complex as prior art systems.
Another object is to provide an improved method and system for producing electric power from a thermonuclear fusion reactor that is both safer and more reliable when compared to prior art systems.
Other objects and advantages of the invention will become apparent from the following description and accompanying drawing.